A drive force controller or a traction control system which prevents drive wheels from slipping during acceleration of a vehicle so as to prevent acceleration performance from falling, for example decreases the output of an engine according to slip of the drive wheels.
This decrease in output is obtained for example by closing the opening of a second throttle which is disposed in an intake passage of the engine in series with the first throttle, stopping injection of fuel to specific cylinders, or retarding a fuel ignition timing.
Tokkai Hei 8-144803 published by the Japanese Patent Office in 1996, discloses a drive force controller for a lean burn engine in which combustion is performed at a leaner air-fuel ratio than a stoichiometric air-fuel ratio, and fuel cut is performed by stopping fuel injection to specific cylinders of the engine.
However when the lean burn operation of the engine is performed in parallel with the fuel cut operation, the engine operation is apt to become unstable. Especially, in case the lean burn system is adopted in a direct injection gasoline engine wherein gasoline is directly injected into a cylinder, fuel cut operation easily causes unstable engine operation. In such an engine, uniform combustion is performed at an ordinary air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio, and stratified combustion is performed with a lean air-fuel ratio. The air-fuel ratio in stratified combustion is even leaner than the lean air-fuel ratio of an ordinary lean burn engine, and stratified combustion therefore requires a large intake air volume.
Therefore, when throttle operation was performed during fuel cut in the stratified combustion state, the engine running state may become even more unstable.
The output reduction of the engine due to fuel cut may also become excessive when there are only a few cylinders in the engine.